Process for imparting oil repellency to suede leather

ABSTRACT

A PROCESS FOR IMPARTING OIL REPELLENCY TO THE SURFACE OF SUEDE LEATHER WHICH COMPRISES ADDING TO SAID SUEDE LEATHER DURING THE DRY TUMBLING THEREOF A FLUOROCHEMICAL IN-PARTICULATE FORM AS A DRY POWER OR AS SUSPENDED OR EMULSIFIED PARTICLES IN WATER, THE AMOUNT OF ADDED WATER NOT EXCEEDING ABOUT 7 WEIGHT PERCENT OF THE TOTAL SUEDE LEATHER WEIGHT, SAID FLUOROCHEMICAL BEING CAPABLE OF IMPARTING OIL REPELLENCY TO LEATHER AND HAVING A MELTING POINT BELOW 200*C., AND TUMBLING SAID LEATHER UNTIL SAID FLUOROCHEMICAL IS UNIFORMLY DISTRIBUTED OVER THE SUEDE SURFACE.

United States Patent 3,573,952 PROCESS FOR IMPARTING OIL REPELLENCY T0SUEDE LEATHER Thomas W. Berger, Roseville, Minn., assignor to MinnesotaMining and Manufacturing Company, St. Paul,

Minn.

N0 Drawing. Filed Oct. 21, 1968, Ser. No. 769,358 Int. Cl. B44d 1/094,1/32 US. Cl. 117-16 6 Claims ABSTRACT OF THE DISCLOSURE This inventionrelates to a novel process for the application of fluorochernicalmaterials to suede leather. In one aspect this invention relates to anovel process in which the surface of suede leather can be rendered oiland water resistant during the suede manufacturing process.

In the production of garment suede leathers the finishing operations aredesigned to produce a napped material which is soft to the touch andappealing to the eye. One outstanding characteristic of a fine suedeleather is its ability to track, i.e. to give a lighter or darkerappearance to the surface as the suede is stroked or touched. Anyfinishing operation which diminishes either the soft feel or the abilityto track is considered to diminish the value of the finished suedeproduct. The ordinary tanning and treating of leather includes theintroduction of fat or oil in a fat liquoring step and frequentlyincludes a treatment of the suede leather to impart stain repellency.Commonly included in the finishing of suede leathers are such waterrepellent materials as chromium complexes, silicone oils, and variousfiuorochemicals, such as the fluorochemical chromium complexes andfluorine containing urethane resins, which provide not only waterrepellency but stain repellency as Well and which further permit thesuede to be washed.

In the preparation of stain repellent suede leathers the material isnormally fat liquored and often given further water repellent treatmentsby using silicones, chromium complexes and, occasionally, an emulsifiedurethane material. These treatments are normally conducted in a wettanning drum. After drying the leather is bufied to provide the suedesurface. The suede skins are then placed into a drum in which they aretumbled for a period of time to soften the skins and to free them ofdust, short fibers, dye particles, etc. by passing air through the drumduring the tumbling operation. During the bufiing and tumbling stepsmany untreated or lightly treated fibers on the suede surfaces areexposed, and the resulting surface readily accepts oil stains andfingermarks. To eliminate this problem it has become customary toprovide a top spray treatment in which a dilute solution of afiuorochemical in a volatile organic solvent is sprayed over the surfaceof the suede material, and the solvent is then evaporated. In order toobtain uniform coverage with an economically small amount offluorochernical relatively large quantities of solvent must be applied,and solvent removal is usually conducted in an oven with ice the exhaustgases passing through a solvent recovery system. In addition to theexpense of providing and maintaining such solvent recovery systems andthe expense incurred by the unavoidable loss of at least some of theorganic solvent, this treatment also tends to produce a suede with asomewhat harsher feel than the suede material immediately after tumblingand usually with a significant loss in the ability of the surface totrack. The top spraying of suede materials from organic solvent systemsis, therefore, to be avoided whenever possible. Although aqueuossolutions or suspensions of fluorochemicals have been tried as a topspray on a dry suede material after tumbling, the large quantities ofwater necessary to uniformly distribute the fluorochemicals results in avery wet skin. Since rapid drying of wet suede materials would causethem to harden, only slow and controlled drying is permissible, duringwhich time mildew or spoilage can occur. At best, the resulting suedeleather is unacceptable due to the relatively harsh feel. In the topspray treatment attempts to minimize the damage by decreasing the amountof organic solvent or water produces an uneven distribution of thefiuorochemical and consequently produces spotty results and a productwith less than desirable soil resistance.

It has now be en found that the top spray treatment of suede leatherscan be replaced by the addition of a fiuorochemical capable of impartingoil repellency to leather to the water repellent suede material duringthe tumbling operation. Two critical conditions must be observed. First,the fiuorochemical must be applied in particulate form and the particlesmust be capable of being uniformly distributed over the surface fibersof the suede leather during the tumbling operation. The particles offluorochernical material can be obtained and used as a dry powder or asthe emulsified or suspended phase in an aqueous emulsion or suspension.In each instance the fluorochernical particulate material, whether as adry powder or an emulsion or suspension, can be introduced directly intothe drum during the tumbling of the suede materials. It is unexpectedthat the fluorochernical particulates could be made to uniformly treatthe water repellent suede surfaces in a tumbling drum. It appearsprobable that the fiuorochemical treatment provides a substantiallycontinuous film or fluorochemical over the suede surface. When using asmall amount of fluorochemical the particle size should be as small aspossible to permit adequate and uniform coverage over the entire surfaceduring the tumbling operation. Small particle size may be provided byfine grinding of the dry fluorochemical, such as by passage through amicropulverizer. Alternatively, small particle size fiuorochemicalmaterials are inherently provided in an aqueous emulsion or suspension.In the alternative case, under the conditions prevailing in the tumblingdrum, the aqueous medium is evaporated at such a rate that the particlesdo not have an opportunity to coalesce and are therefore distributeduniformly over the fiber surface. By contrast, the use of a solution offiuorochemical in an organic solvent has been found to provide veryunsatisfactory and non-uniform treatment of the suede surface,apparently because the solvent is absorbed into the suede surface andcarries the fluorochernical with it, thereby providing less time for thefiuorochemical to be redistributed over the suede surface duringtumbling. However, since the suede materials are substantially waterrepellent, due to the prior treatment with fat liquor, silicones,chromium complexes, etc., the water of the emulsion or suspension doesnot penetrate into the surface but remains thereon until it is removedby evaporation during tumbling. As tumbling continues and the solvent isremoved, the fluorochernical particulate material is distributed overthe surface by the motion of the hides and the heat generated during thtumbling.

Even with fiuorochemical material of a relatively large particle size,the powdered material is readily distributed during the tumblingoperation if the fiuorochemical itself has a melting point below about200 (3., preferably below 150 C. If the fiuorochemical particulatematerial has a melting point below about 50 C. it is diflicult orimpossible to grind the solids to an extremely fine particle size. Forthose materials melting below about 100 C. it is possible to mix thesolid with granulated, solid carbon dioxide while it is being passedthrough a micropulverizer, and the material is then sufficiently brittleto permit further pulverization to occur.

In carrying out this invention in its preferred aspect, using an aqueousemulsion or suspension, the amount'of water is important. The use ofexcess water will produce a wet leather having poor characteristics, asmentioned earlier. Accordingly not more than about 7 weight percent ofwater, based on the weight of the suede leather in the drum, is appliedduring the tumbling operation. Preferably as little water is used aspossible and, in general, between about 1.5 and 4 weight percent ofwater is added. The amount of the fiuorochemical particulate materialadded, either as a dry powder or in a suspension or emulsion, dependsupon the thickness of the skins, the particular set of tanningconditions, colorants, etc., but at least about 0.05 weight percent offiuorochemical, based on the total weight of suede material, isnecessary to provide satisfactory stain resistance, and no appreciableadvantage is obtained with amounts much in excess of about 1 weightpercent.

Many different types of fluorochemicals useful in treating leather foroil or stain repellency have been de scribed in the literature, and anyof these having suitable melting points may be used in this invention.The most useful fluorochemicals are those having a perfluoroaliphaticgroup containing at least three carbon atoms, preferably no more thanabout twenty carbon atoms, and a terminal trifiuoromethyl group. Theperfluoroaliphatic chain may also contain nitrogen or oxygen atomsbonded only to carbon atoms, without significantly affectingperformance. The presence of an occasional hydrogen or chlorine atom inthe fluoroaliphatic group is not particularly harmful, but aperfiuoroaliphatic radical is much preferred. To obtain reasonable oilrepellency the fiuorochemical compound should have at least aboutpercent by weight of fluorine in the form of fluoroaliphatic radicals.Suitable compounds can be prepared with up to 60 weight percent orhigher of fluorine, but generally those containing between about 30 and50 percent fluorine have been found most satisfactory. The exactchemical structure of the fiuorochemical has not been found to becritical in the practice of this invention, and any of the variousfluorochemicals in particulate form which otherwise meet the meltingpoint requirements and which are of value in imparting stain repellencyto leather can be used in the practice of this invention. In general,one or more polar groups, such as ester groups, amide groups, oraromatic rings, are necessary in such fiuorochemical compounds toprovide a material melting in the preferred range. Extremely highmolecular weight polymers generally have unacceptably high meltingpoints, and completely non-polar materials generally have unacceptablylow melting points. When a fiuorochemical polymer is used it should besubstantially free of crosslinking and must be truly thermoplastic inorder for it to be distributed over the suede surface during tumbling. Alow percentage of crosslinking is permissible, provided the materialflows readily at a temperature below about 200 C. Although no externalheat is necessary during the tumbling operation, the continuous impact,twisting and folding of the suede materials during the tumblingoperation apparently generates suf- 4 ficient internal heat to permitrelatively uniform distribution of the fiuorochemical over the suededsurfaces.

Amide derivatives having a perfluoroaliphatic radical, includingurethanes, have been found to be a particularly preferred class offiuorochemicals for the practice of this invention. Such materials bondquite readily to the fiber, are sufficiently low melting to be readilyspread into a continuous film and characteristically remain on the fiberdespite extended and prolonged abrasion, such that the effect of thetreatment continues during actual use of the sueded product. Unless thefiuorochemical material is modified to allow for crosslinking afterapplication, such materials are not particularly resistant to removal bydry cleaning solvents. However, the presence of, for example, N-methylolgroups or conjugated diene groups in relatively low occurrence canprovide sufficient crosslinking sites to permit some crosslinking tooccur after the tumbling treatment, thereby providing more substantialresistance to dry cleaning solvents and provide a more permanenttreatment.

The experiments to be described were carried out in a dry mill or drumsomewhat smaller than is usually employed in actual commercial practice.The dry mill consisted of a wooden drum, approximately 8 feet indiameter and 4 feet long, supported on hollow gudgeons through which afinely divided spray of the aqueous emulsions could be introduced. Thesolid fiuorochemical particulate materials were added by placing in thedrum an open paper bag containing the desired amount of thefluorochemical powder. The working load of the drum consisting of about90 pounds of essentially dry suede leather (dry leather normallycontains about 15 percent by weight moisture), equivalent toapprozimately 550 square feet of sueded side material. The drum wasrotated at about 15 /2 revolutions per minute. The fiuorochemicals wereadded in an amount of about 0.25 grams per square foot of the suededsurface, either dry or dispersed in an appropriate liquid medium.

The materials were prepared by standard processes. As an example, theemulsion of Run II was prepared by charging 18.5 parts of solid urethane(prepared in accordance with the method of Example 3 of U.S. 3,398,-182) to a 25 gallon glass lined stirred jacketed reactor, along with 42parts of ethyl acetate, 0.75 part of a polyoxyethylene sorbitanmonooleate non-ionic emulsifier and 0.75 part of a complex organicphosphate ester anionic emulsifier. The charge was heated with agitationto 60 C. 63 parts of water containing 0.4 part of an alkylarylsulfonateanionic surfactant, preheated to 60 C., was slowly added with stirring.The suspension so formed was passed through a homogenizer until a stablecreamy emulsion was formed. The emulsion was then returned to thereactor, further diluted with parts of water, heated to 65 C., and ethylacetate volatilized by a mild reduction of pressure, care being taken toavoid foaming. Heating was continued up to 85 C., at which point theethyl acetate was substantially removed. The pH of the emulsion wasadjusted to 8 with 20 percent ammonium hydroxide. Before addition to thetumbling drum the emulsion was further diluted with Water to a 9 percentsolids content. The particular emulsifiers used in preparing aqueousemulsions of the fluorochemicals are not critical and depend upon theparticular fiuorochemical being emulsified. In some cases, excellentresults have been obtained with the non-ionic emulsifier alone, and inother cases a combination of a non-ionic emulsifier and a cationicsurfactant, such as C F SO NH'C H N(CH Cl has proven effective asstabilizer. Generally from 2 to 12 percent by weight of emulsifier isused, on the basis of the fiuorochemical particulate material. Polymericlatices were prepared generally as indicated in U.S. 3,062,765, anddiluted to the appropriate concentration. Powdered solids were preparedby drying solutions or latices at about 25-50 C. under vacuum. Theresulting solids were reduced by passage through a micropulverizer toproduce a powder with a particle size distribution from about 100 toless than 2 microns, with a major fraction of the particles between 20and 50 microns.

was then used to provide a fine powder and another part of this emulsionwas dried to provide a solid which was dissolved in xylene hexafluoride.The polymeric particles TABLE I Properties of treated suede Meltingpoint, Oil Spray Abrasio n Run Chemical 0. Form rating rating resistance II I [CaFnS O2N(CH3)CH2CH2OCHNH]2[(C0H4)2CH2] 195 Powder 65 80 55 IIII..." [CaF S O2N C2H5 OH CHzOCN hweHaCHfl 105-115 9% aqueous emulsion70 85 55 II III. [CKF S OzN(C2H CHzCH2OCNH12ICaHaCH 105-115 Powder 70 8060 H IV-- [C F S O2N(CH )CHzCHNH]a[CsH4CH2CeH3CH2CsH4] 125 ....-do 55 9050 II II V.-. [CsF S O2N(OH3)CHZOH2CN ]2[CflH4CH2C6H3CH2C0H-1NHCC18H37]85 9% aqueous 011111181011- 75 80 50 ll ll VI---- [053F175 O2N(CH3)CH2CH2CNH]2[C6H4CH2C6H3CH2CBHJNHCCISHQY] 85 5%cigllglcog 1n 0 0 a 3.VII. C1Fi5CO2H.Cr(OH) C12 (Werner Complex) 0 80 0 VIII CgFgSO K 0 70 0ll IX CBF17CO2N(CH3) CHZCHZOCCH=CII2 Homopolymer 95-100 do 0 80 0 HX.--" C8F11C O2N(CH CHzCHzO C CH CH2 Homopolymer 95-100 9% aqueousemulsion 50 80 50 ll XI. C F C OzN(CH CH2CH2O C CH= CH2 Homopolymer95-100 5% solution in 0 80 0 CeHK FaM' II XII Copolymer of 05F 11G OzNCH3) CHzC H20 0 CH C H2 and butyl 80-100 9% aqueous emulsion. 50 80 50acrylate (90:10 mol ratio). XIIL Control-no top coat 0 80 0 OILREPELLENCY \RATING SCALE Oil repellency Percent n-heptane in mineralrating oil-heptane mixture (by vol.) 100 50 60 10 5O O 0 (No holdout tomineral oil) The abrasion resistance of the test samples is measured byrepeating the Oil Repellency Test after the suede surface has beenstroked ten times in one direction with a brass wire brush. Thisprovides an indication of the durability of the treatment during normalgarment or shoe manufacturing processes, and subsequent wear.

Examination of Runs IX, X and XI in the table illustrates the proceduresof this invention. The same material is used in these three runs and wasinitially prepared in the form of an emulsion. Some of this emulsion inthe aqueous emulsion had an average particle size of less than twomicrons. When, as in Run X, the emulsion was sprayed onto suede leatherwhile it was rotating and tumbling in the drum, the water apparentlyevaporated and very fine particles remained on the surface. Thisparticular polymer has been found to flow readily at a temperature of100 C. Under the conditions of strong mechanical agitation andcontinuous tumbling contact of the suede surfaces the particlesevidently are able to flow and form a substantially continuous filmsufiicient to impart oil repellency which is retained even after severeabrasion. When the same polymer was dissolved in solvent and applied tothe material, very poor oil repellency results were obtained, apparentlybecause the solution was readily absorbed into the leather.

The distinction between emulsion and solution treatment is indicated inRuns V and VI, where the polyurethane material provides excellent oilresistance when applied from an emulsion but no perceptible improvementwhen applied from solution.

Even with relatively large particle size, powdered materials having amelting point below about 200 C. provide excellent treatment, as shownin Runs I, III and IV, whereas higher melting materials provide littleor no effective treatment, as shown in Runs VII and VIII.

It would be possible to use an extremely low boiling solvent, such asdichlorodifluoromethane, as the dispers ing medium for thefluorochemical, and the rapid evaporation of such solvents shouldprovide a finely dispersed fluorochemical particulate on the suededsurface. However, such solvent systems would be obviously difficult tocontrol and would have the same problems of high cost and air pollutioninherent in the solution methods presently in use.

What is claimed is:

1. A process for imparting oil repellency to the surface of suedeleather which comprises adding to said suede leather during the drytumbling thereof a fluorochemical in particulate form as a dry powder oras suspended or emulsified particles in water, the amount of added waternot exceeding about 7 weight percent of the total suede leather weight,said fiuorochemical being capable of imparting oil repellency to leatherand having a melting point below 200 C., and tumbling said leather untilsaid fluorochemical is uniformly distributed over the suede surface.

2. The process of claim 1 in which said particulate form is a drypowder.

3. The process of claim 1 in which said particulate form is suspendedparticles of an aqueous suspension.

4. The process of claim 1 in which said particulate form is emulsionparticles of an aqueous emulsion.

5. The process of claim 1 in which said fluorochemical has a meltingpoint between 50 C. and 150 C.

6. The process of claim 1 in which said fiuorochemical is present in anamount of at least 0.05 percent of the weight of said suede leather.

References Cited UNITED STATES PATENTS WILLIAM D. MARTIN, PrimaryExaminer R. M. SPEER, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,573952 Dated April 6 1971 Inventor(s) Thomas W. Berger It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Columns 5 and 6, TABLE I, items: IX, X, XI and XII,

I "C F CO should be C F SO Columns 5 and 6, TABLE I, item XII, "(90=l0mol ratio)" should be -(90:1O mol ratio)-- Signed and sealed this 21stday of September 1971.

(SEAL) Attest:

EDWA Q J ROBERT GOTTSCHALK Attesting Offlcer Acting Commissioner of P211FORM POJOSO (10-69] LJSCOMM-DC cos

